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askthe higher up the tubing wall than the other. Also, solid debris inside the tubing—sand, cobwebs, dust—can cause the water levels to be different. The same goes for liquid residue; if the tube has had oil, soap, or another liquid in it, the residue can mix (or not) with the water and cause mismatched menisci. There can’t be any bubbles of air in the water. I have found that the best way to get a bubble-free fill is to siphon water from a pail rather than holding the tube under a faucet, where the water stream can contain tiny air bubbles. To clear air bubbles, you need to hold the ends of the tubing high so that the tubing is completely suspended—and then wait. It can take a few minutes for tiny bubbles to rise out of a narrow-diameter tube. At a twostory house, I hang the tubing out a second-story window. Tapping the tubing lightly can help the air bubbles move upward rather than clinging to the side. Water-level issues I’m framing a house and need to level the mudsills. I don’t have a laser, and it isn’t in the budget, so I’m using some clear plastic tubing I’ve had for a while as a water level. My problem is that the ends of the water in the 30-ft.-long tube are about 1⁄2 in. off. Any thoughts on what I’m doing wrong and how to correct it? —Carlos via email M.G.: Water seeks level even in a long hose, and assuming that you haven’t just discovered you are 1⁄2 in. out of level, there are a few conditions that can skunk you. First, the hose needs to have an inside diam- eter of at least 3⁄8 in. I’ve tried using 1⁄4-in. tubing, and for some reason the meniscus at one end can climb 84 FINE HOMEBUILDING Photos this page: top, andy engel; bottom, rob Yagid The temperature of the water matters, too. Make sure that part of the tubing isn’t exposed to sun for long periods while another part is in the shade. Lastly, check the ends periodically to make sure the water levels match. Open-cell vs. closed-cell foam To insulate 2x4 walls and 2x6 rafter bays, a spray-foam contractor suggested closed-cell foam since I don’t have a lot of framing depth and need to hit certain R-values. I thought open-cell foam was preferred when insulating roof decks and some walls. I’m using closedcell in the basement, but is it also best upstairs, particularly against the roof deck? —Kurt McInness new Hartford, Conn. Martin Holladay: In unvented roof assemblies, open-cell foam has been associated with damp roof sheathing and sheathing rot, so closed-cell foam is usually preferred for this application. Closed-cell foam has a higher R-value per inch and is vapor impermeable. It also will perform better below or above grade. Cold-climate builders using open-cell foam in an unvented roof assembly can reduce the chance of damp roof sheathing by installing drywall painted with vapor-retarder paint. Hot-climate builders need to heat the attic during the winter and cool it during the summer.